Ian Mackay. Quantitative Genetics and Heterosis скачать в хорошем качестве

Ian Mackay. Quantitative Genetics and Heterosis

Dispersion of favourable alleles is common: in its absence genetic progress is not possible since progeny with better performance than parents will not be found. If the loci responsible also show directional dominance, then hybrids which exceed the performance of the parents will occur: population and quantitative genetics theory tells us heterosis is inevitable with dominant gene action and dispersion of favourable alleles. Other genetic factors can augment the magnitude of heterosis. In plant breeding, heterotic groups are often described as necessary. Crosses between lines from different groups show greater levels of heterosis than crosses within groups. Groups may pre-exist but even in their absence they can be selected for. The advocacy of new molecular mechanisms for heterosis must be judged against these straightforward theoretical and empirical facts from population and quantitative genetics. If new classes of genetic and epi-genetic variation contribute to trait variation and also show dominance, their contribution to heterosis is assured. The search for an explanation of 'the mystery of heterosis' seems likely to continue. Meanwhile, the future of plant breeding will be determined by the irresistible rise of 'genomic selection', which has appropriately been called 'The Quantitative Geneticists' Revenge'.